In recent years, as the numbers of hybrid vehicles and idling stop vehicles increase, exhaust gas from a vehicle that stops an engine during driving tends to be measured.
As a conventional exhaust gas analyzer, as disclosed in Patent literature 1, there is one that directly samples exhaust gas from a tail pipe through which the exhaust gas from an engine flows, and introduces the sampled exhaust gas into an exhaust gas analyzer.
However, in the case of using the exhaust gas analyzer to measure exhaust gas of the above hybrid vehicle or the like, even if an engine is stopped, suction by a pump of the exhaust gas analyzer is applied. If so, inside the engine and a tail pipe, a gas flow that is different from a primary flow occurs, which may cause a problem, for example, a temperature of a catalyst provided in the tail pipe is changed, pressure of an exhaust port of the engine is reduced, or other problem.
At this time, it is thought that simultaneously with the engine stop, the pump of the exhaust gas analyzer is stopped to stop the measurement; however, in the case of stopping the pump, there occurs a problem that the gas suction is not instantaneously stopped due to inertia of the pump to create negative pressure inside pipes such as the engine and tail pipe, and thereby an engine condition is changed, a load is placed on the pump itself of the analyzer, or the gas unexpectedly flows, or other problem. Also, after the stop of the pump of the exhaust gas analyzer, if the pump is activated simultaneously with the start of the engine, a delay in rise of the pump or the like is of concern.